We will determine as much as possible of the amino acid sequence of the constant region of the delta chains of human IgD. IgD myeloma proteins will be analyzed because they are the only source of relatively large amounts of serum secreted IgD. Particular emphasis will be placed on establishing the sequence of the inter-Fd-Fc ("hinge") region of the delta chain, because it bears an accumulation of basic residues, which is unique among Ig heavy chains and is probably responsible for IgD's great susceptibility to enzymatic degradation. Preliminary experiments showed that delta chains yield 3 cyanogen bromide (CNBr) fragments that are derived from th constant region. These fragments will be isolated and their NH2-terminal sequence determined by automated sequencing. Finally, the characterization of the CNBr fragments will be completed by conventional methods of amino acid sequencing emoploying substractive Edman degradation of enzymatically derived peptides. Simultaneously with the sequence analyses, cell bound IgD and its delta chains will be isolated from cultured human lymphoblastoid Wil-2WT cells, and we will attempt to compare certain of the Wil-2WT delta chain structures with those of myeloma delta chains. In particular, we will investigate the cell bound delta chains for a COOH-terminal methionine residue like that in meloma delta chains and determine whether they have the same half-cystine containing peptides involved in the inter-heavy-light and inter-heavy-heavy chain disulfide bonds since these two characteristics are clearly established in the myeloma delta chain.